Method and apparatus for performing contention-based access in a mobile communication system

ABSTRACT

The present invention relates to a method and apparatus in which a terminal performs contention-based access in a mobile communication system, wherein the method comprises: a sensing step of sensing whether or not contention-based access is allowed for at least one logical channel; a receiving step of receiving a contention-based reverse grant from a base station; and a transmitting step of transmitting data to the base station through the logical channel for which the contention-based access is allowed. According to the present invention, contention-based access can be efficiently performed, and the reliability of transmission can be ensured.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 15/971,361, filed on May 4, 2018, and continuation of priorapplication Ser. No. 13/514,488, filed on Jun. 7, 2012, which issued asU.S. Pat. No. 9,967,901 on May 8, 2018; which was the National Stage ofInternational application PCT/KR2010/008788 filed on Dec. 9, 2010; whichclaimed priority under 35 U.S.C § 119(a) of a Korean patent applicationnumber 10-2009-0123138, filed on Dec. 11, 2009, in the KoreanIntellectual Property Office, the disclosure of each of which isincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a mobile communication system and, inparticular, to a method and apparatus for performing contention-basedaccess in a mobile communication system.

Description of the Related Art

Mobile communication systems have developed to provide the subscriberswith voice communication services on the move. With the advance oftechnologies, the mobile communications have been evolved to supporthigh speed data communication services as well as the standard voicecommunication services.

Recently, as one of the next generation mobile communication system,Long Term Evolution (LTE) is on the standardization by the 3rdGeneration Partnership Project (3GPP). LTE is a technology designed toprovide high speed packet-based communication of up to 100 Mbps andaimed at commercial deployment around 2010 timeframe. As the LTEstandard is on the verge of ratification, discussion is focused onLTE-advanced (LTE-A) with the adoption of various novel techniques toLTE. One of these novel techniques is the contention-based access.

Typically, since uplink transmission is performed through the dedicatedresource allocated by a base station, collision does not take place inuplink transmission. In order to allocate transmission resourcededicatedly, however, the terminal has to request the base station fortransmission resource allocation, resulting in increase of transmissiondelay. In order to overcome this problem, the base station may use apart of the transmission resource as contention-based access resource.The transmission resource known as contention-based access resource isfreely used by the terminals having data to transmit. In uplinktransmission using the contention-based transmission resource, collisionis inevitably due to transmission attempts of a plurality of terminals.Since the contention-based transmission has low transmissionreliability, it may cause significant side effect to allow thecontention-based transmission for all the types of data withoutrestriction.

DISCLOSURE OF INVENTION Technical Problem

The present invention has been made in an effort to solve the aboveproblem and it is an object of the present invention to provide acontention-based uplink transmission method and apparatus that iscapable of improving uplink transmission efficiency of thecontention-based transmission resource and guaranteeing transmissionreliability.

Solution to Problem

In order to solve the above problem, a contention-based access executionmethod of a terminal in a mobile communication system includes adetection step of detecting whether contention-based access is allowedfor at least one logical channel; a reception step of receiving acontention-based uplink grant from a base station; and a transmissionstep of transmitting data on a logical channel on which thecontention-based access is allowed. In this case, the whether to allowthe contention-based access is notified to the terminal by the basestation through signaling (control message) or preconfigured between theterminal and base station at initial stage.

According to an embodiment of the present invention, the terminal mayterminates the contention-based uplink transmission when thecontention-based uplink transmission collides with Random AccessPreamble transmission or message 3 transmission.

In accordance with another aspect of the present invention, Acontention-based access execution method of a terminal in a mobilecommunication system includes a step of checking, when data to betransmitted occurs, whether data to be transmitted through SignalingRadio Bearer 0 (SRBO) channel exists, a step of terminating, when thedata to be transmitted through the SRBO channel, monitoring receipt of acontention-based uplink grant from a base station, and a step ofmonitoring, when the data to be transmitted through the SRBO channel,receipt of the contention-based uplink grant from the base station.

In order to solve the above problem, a terminal for performingcontention-based access in a mobile communication system includes atransceiver which transmits and receives data or control informationthrough a radio channel, and a contention-based access controller whichcontrols detecting whether contention-based access is allowed for atleast one logical channel, receiving a contention-based uplink grantfrom a base station, and transmitting data on a logical channel on whichthe contention-based access is allowed. In this case, the whether toallow the contention-based access is notified to the terminal by thebase station through signaling (control message) or preconfiguredbetween the terminal and base station at initial stage.

According to an embodiment of the present invention, the terminal mayterminates the contention-based uplink transmission when thecontention-based uplink transmission collides with Random AccessPreamble transmission or message 3 transmission.

In accordance with another aspect of the present invention, a terminalfor performing contention-based access in a mobile communication systemincludes a transceiver which transmits and receives data or controlinformation through a radio channel, and a contention-based accesscontroller which controls checking, when data to be transmitted occurs,whether data to be transmitted through Signaling Radio Bearer 0 (SRB0)channel exists, terminating, when the data to be transmitted through theSRB0 channel, monitoring receipt of a contention-based uplink grant froma base station; and monitoring, when the data to be transmitted throughthe SRB0 channel, receipt of the contention-based uplink grant from thebase station.

ADVANTAGEOUS EFFECTS

The present invention is capable of performing contention-based accessefficiently while securing transmission reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a structure of the LTE mobilecommunication system.

FIG. 2 is a diagram illustrating a protocol stack of the LTE system towhich the present invention is applied.

FIG. 3 is a signaling diagram illustrating conventional uplinktransmission procedure in the LTE mobile communication system.

FIG. 4 is a signaling diagram illustrating a contention-based accessoperation briefly.

FIG. 5 is a signaling diagram illustrating the contention-basedtransmission procedure according to the first embodiment of the presentinvention.

FIG. 6 is a flowchart illustrating an operation order of the UEaccording to the first embodiment of the present invention.

FIG. 7 is a signaling diagram illustrating a contention-basedtransmission procedure according to the second embodiment of the presentinvention.

FIG. 8 is a flowchart illustrating a procedure of the UE according tothe second embodiment of the present invention.

FIG. 9 is a flowchart illustrating a procedure of the UE 715 accordingto the second embodiment of the present invention.

FIG. 10 is a flowchart illustrating a procedure of the UE according tothe third embodiment of the present invention.

FIG. 11 is a flowchart illustrating a procedure of the UE according tothe fourth embodiment of the present invention.

FIG. 12 is a flowchart illustrating a procedure of the UE according tothe fifth embodiment of the present invention.

FIG. 13 is a flowchart illustrating a procedure of the UE according tothe sixth embodiment of the present invention.

FIG. 14 is a flowchart illustrating a procedure of the UE in expiry ofTpollretransmit according to the sixth embodiment of the presentinvention.

FIG. 15 is a block diagram illustrating the UE according to theembodiment of the present invention.

FIG. 16 is a block diagram illustrating the UE RLC entity according tothe sixth embodiment of the present invention.

FIG. 17 is a block diagram of the eNB according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention are described withreference to the accompanying drawings in detail. The same referencenumbers are used throughout the drawings to refer to the same or likeparts. Detailed descriptions of well-known functions and structuresincorporated herein may be omitted to avoid obscuring the subject matterof the present invention.

The present invention proposes a method and apparatus for guaranteeingreliability in uplink transmission through contention-based accesstransmission resource in which a terminal select the data to betransmitted in contention-based uplink transmission and transmit thedata in uplink.

Before starting the explanation of the present invention, a descriptionis made of the LTE mobile communication system with reference to FIGS.1, 2, and 3. FIG. 1 is a diagram illustrating a structure of the LTEmobile communication system.

Before starting the explanation of the present invention, a descriptionis made of the LTE mobile communication system with reference to FIGS.1, 2, and 3.

FIG. 1 is a diagram illustrating a structure of the LTE mobilecommunication system.

Referring to FIG. 1, the radio access network of the mobilecommunication system includes evolved Node Bs (eNBs) 105, 110, 115, and120, a Mobility Management Entity (MME) 125, and a Serving-Gateway(S-GW) 130. The User Equipment (hereinafter, referred to as UE) 135connects to an external network via eNBs 105, 110, 115, and 120 and theS-GW 130.

The eNBs 105˜120 correspond to legacy node Bs of Universal MobileCommunications System (UMTS). The eNBs 105, 110, 115, and 120 allow theUE to establish a radio link and are responsible for complicatedfunctions as compared to the legacy node B. In the LTE system, all theuser traffic including real time services such as Voice over InternetProtocol (VoIP) are provided through a shared channel and thus there isa need of a device which is located in the eNB to schedule data based onthe state information such as UE buffer conditions, power headroomstate, and channel state. Typically, one eNB controls a plurality ofcells. In order to secure the data rate of up to 100 Mbps, the LTEsystem adopts Orthogonal Frequency Division Multiplexing (OFDM) as aradio access technology. Also, the LTE system adopts Adaptive Modulationand Coding (AMC) to determine the modulation scheme and channel codingrate in adaptation to the channel condition of the UE. The S-GW 130 isan entity to provide data bearers so as to establish and release databearers under the control of the MME 125. MME 125 is responsible forvarious control functions and connected to a plurality of eNBs.

FIG. 2 is a diagram illustrating a protocol stack of the LTE system towhich the present invention is applied.

As shown in FIG. 2, the protocol stack of the LTE system includes PacketData Convergence Protocol (PDCP) 205 and 240, Radio Link Control (RLC)210 and 235, Medium Access Control (MAC) 215 and 230, and Physical (PHY)220 and 225. The PDCP 205 and 240 is responsible for IP headercompression/decompression, and the RLC 210 and 235 is responsible forsegmenting the PDCP Protocol Data Unit (PDU) into segments inappropriate size for Automatic Repeat Request (ARQ) operation. The MAC215 and 230 is responsible for establishing connection to a plurality ofRLC entities so as to multiplex the RLC PDUs into MAC PDUs anddemultiplex the MAC PDUs into RLC PDUs. The PHY 220 and 225 performschannel coding on the MAC PDU and modulates the MAC PDU into OFDMsymbols to transmit over radio channel or performs demodulating andchannel-decoding on the received OFDM symbols and delivers the decodeddata to the higher layer. In view of transmission, the data input to aprotocol entity is referred to as Service Data Unit (SDU), and the dataoutput by the protocol entity is referred to as Protocol Data Unit(PDU).

FIG. 3 is a signaling diagram illustrating conventional uplinktransmission procedure in the LTE mobile communication system.

If a predetermined condition such as occurrence of transmission data isfulfilled, the UE 305 sends the eNB a scheduling request to request fortransmission resource (315). Hereinafter, when it becomes necessary totransmit the scheduling request, it is expressed as “scheduling requestis triggered,” and the terms “scheduling request” and “SR” are usedinterchangeably. A scheduling request is classified into one ofDedicated Scheduling Request (D-SR) and Random Access Scheduling Request(RA-SR). D-SR is the scheduling request transmitted on the dedicatedtransmission resource allocated to the UE. The D-SR transmissionresource is the dedicated transmission resource arriving periodically tocarry 1 bit information. The UE occupying the D-SR transmission resourcetransmit D-SR when it is necessary to transmit scheduling request. D-SRtransmission resource may not be allocated all the UEs, and the UEhaving no D-SR transmission resource notifies the eNB of the occurrenceof transmission data through random access procedure, i.e. RA-SRtransmission.

Upon receipt of the scheduling request signal, the eNB 310 allocatesuplink transmission resource to the UE 305. The uplink transmissionresource is allocated by means of an uplink grant which is transmittedto the UE 305 on Physical Downlink Control Channel (PDCCH) (320). Theuplink grant includes a Cell-Radio Network Temporary Identity (C-RNTI)as the UE identifier so as to be addressed to the UE allocated theC-RNTI. The uplink grant includes information on the transmissionresource for the uplink transmission of the UE 305 and MCS to be appliedto the uplink transmission and the information necessary for HARQoperation such that the UE 305 performs uplink transmission at a timepoint elapsed a predetermined period since the time point when theuplink grant has been received according to the information. As far asthe UE 305 has the data to transmit, the eNB 310 may continuetransmitting the uplink grant to the UE.

FIG. 4 is a signaling diagram illustrating a contention-based accessoperation briefly.

The eNB 410 determines scheduling the contention-based accesstransmission resource at certain timing (415). This timing is of thecase where the load of the cell is not heavy and there is the resourceremained without being allocated to UEs. The contention-based accesstransmission resource is the transmission resource allocated tounspecific UEs so as to be allocated with pre-notified (or informed tothe UE in connected state individually) other than C-RNTI. Thisidentifier is referred to as Contention-Based Radio Network TemporaryIdentity (CB-RNTI). The eNB 401 transmits the uplink grant with CB-RNTIat step 420. Hereinafter, the terms “CB-RNTI-identified uplink grant”and “contention-based uplink grant” are used interchangeably. Uponreceipt of the contention-based uplink grant, the UE 405 transmits data,if exist (425), using the contention-based uplink grant (430).

If there is data to be transmitted and if a number of UEs received thecontention-base uplink grant is greater than 1, collision occurs amonguplink transmissions at step 430, resulting in increase of transmissionfailure probability. Also, the contention-based transmission of datarequiring high reliability may cause a significant problem incommunication procedure.

First Embodiment

There are many types of uplink data transmitted from the UE to the eNB,and these uplink data are processed through predetermined logicalchannels respectively. The logical channel is composed of PDCH entityand RLC entity for processing data requiring specific QoS, one logicalchannel is established for one service in general. Accordingly, the datatransmitted or received through one logical channel may having differentimportance or QoS requirement, and the contention-based transmission ofdata on a specific logical channel may not fulfill the QoS required.Representatively, the RRC connection establishment request message orRRC connection re-establishment request message is transmitted through alogical channel referred to as Signaling Radio Bearer (SRB) 0 of whichRLC entity operates in RLC Transparent Mode (TM) and does not supportARQ. If an important control message transmitted in RLC TM istransmitted in contention-based scheme, this may increases the failureprobability of RRC connection establishment procedure or RRC connectionreestablishment procedure. For another example, in VoIP operating in RLCUnacknowledged Mode (UM) supporting no ARQ, if VoIP packets aretransmitted in contention-based scheme the transmission failure causedby collision increases the probability of unsatisfying the requiredtransmission reliability.

The first embodiment of the present invention proposes a method andapparatus for performing contention-based transmission only whenpredetermined conditions are fulfilled, e.g. the contention-basedtransmission causes no redundant padding and transmission powershortage, while ruling out the contention-based transmission of the dataoccurred on a predetermined logical channel, thereby avoidinginefficiency of the contention-based transmission.

FIG. 5 is a signaling diagram illustrating the contention-basedtransmission procedure according to the first embodiment of the presentinvention.

The eNB 510 informs the UE 505 of the contention-based accessavailability per logical channel through a call setup process (515). Asdescribed above, it is preferred to restrict the contention-based accesson the logical channel for which ARQ function is not provided with highdata rate. Instead that the eNB configure the logical channel which doesnot allow contention-based access, it can be another approach to blockthe contention-based access always on a specific logical channel. Forexample, one of the following two rules can be used.

[Rule 1 for Determining Whether to Allow Contention-Based Access PerLogical Channel]

The contention-based access is not allowed for the data occurring on theSRB 0.

According to the determination rule 1, the UE having only the dataoccurred on the SRB 0 neither attempts contention-based access normonitor the CB-RNTI.

[Rule 2 for Determining Whether Allow Contention-Based Access PerLogical Channel]

The contention-based access is not allowed for the data occurring on thelogical channel operating in RLC TM or RLC UM.

According to the determination rule 2, the UE having only the dataoccurring on the logical channel operating in RLC TM or RLC UM neitherattempts contention-based access nor monitors the CB-RNTI.

In case that a logical channel which allows no contention-based accessis designated by the eNB directly rather than a certain rule, the UEneither attempts contention-based access nor monitors the CB-RNTI.

If it is notified that logical channels are configured and which logicalchannels are allowed or not for the contention-based access, the UE 505starts monitoring CB-RNTI when a predetermined condition is fulfilled.If CB-RNTI is monitored, this means to monitor the receipt of an uplinkgrant identified with CB-RNTI on the downlink control channel.

If the contention-based uplink grant is received at step 520, the UE 505configures MAC PDUs using the data on the logical channels with theexception of the logical channels that are not allowed forcontention-based access at step 525. The step for determining the amountof the data to be transmitted per logical channel in match with thetransmission resource and format indicated by the uplink grant isreferred to as logical channel prioritization (LCP) process. The UErules out the logical channels that are not allowed for thecontention-based access in LCP process so as to exclude the data of thelogical channel not allowed for contention-based access from the uplinkdata transmitted in contention-based transmission mode.

The UE 505 checks the amount of padding to be included in the MAC PDU tobe transmitted and the uplink transmission power required in the MAC PDUtransmission to determine contention-based uplink transmission.

FIG. 6 is a flowchart illustrating an operation order of the UEaccording to the first embodiment of the present invention.

The UE 505 discriminate between the logical channels allowed forcontention-based access and the logical channels not allowed forcontention-based access at step 605. Whether to allow contention-basedaccess may be configured based on a control message per logical channelor predetermined for specific logical channels (e.g. SRB 0).

If an uplink grant is received at step 610, the UE determines whetherthe received uplink grant is the contention-based uplink grant or thenormal uplink grant at step 615; and if normal uplink grant, theprocedure goes to step 620 and, otherwise, step 635.

Steps 620, 625, and 630 are the LCP process performed when the UE 505has received the normal uplink grant, and this process is specified insection 5.4.3.1 of the standard technical specification 36.321. Inbrief, the UE 505 allocates resource in amount as much as Bj to thelogical channel having highest priority at step 620. After subtractingthe allocated amount from the entire resource, the remained resource, ifany, is allocated to the channel having the next highest priority asmuch as Bj. The UE 505 repeats this operation until no resource isremained or all of the logical channels are allocated the resource. Thepriority is assigned per logical channel in call setup process in therange from 0 to 7. Bj denotes a token managed per logical channel. Thetoken is used to guarantee the minimum bit rate per logical channel andincreases by a predetermined size every subframe and, if data aretransmitted on the corresponding logical channel, reduced as much as thetransmitted data.

After completing the resource allocation at step 620, the UE deduces theresource allocated in Bj per logical channel at step 625. If there isthe resource remained after allocating for all the logical channelshaving Bj, the UE allocates the remained resource from the logicalhaving the highest priority until the remained resource exhausts. The UEconfigures the RLC PDUs per logical channel in match with the resourcesize allocated per logical channel through PCP process at step 650 andtransmits the RLC PDUs multiplexed in MAC PDUs. If the transmissionresource is left because the allocated resource is greater than the dataamount to be transmission, the remained resource is filled with paddingbits.

If the received uplink grant is the contention-based uplink grant, theUE 505 performs LCP in consideration of only the logical channels onwhich the contention-based access is allowed at step 635. By takingnotice of high transmission failure probability of the contention-basedaccess, Bj is not deduced. The UE 505 allocates resource of the logicalchannels in a descending order of priority of the logical channels, withthe exception of the logical channels on which the contention-basedaccess is not allowed, in size as much as Bj. The resource is deduced asmuch as allocated, and the resource remained after deduction isallocated to the logical channel having the next highest priority asmuch as Bj among the contention-based uplink transmission is allowed.The UE repeats this operation until the resource exhausts or all of thelogical channels having Bj among the logical channel on which thecontention-based uplink transmission is allowed are allocated resources.

As described above, since it is preferred to do not reduce Bj from thecontention-based transmission, the UE 505 skips deducing Bj andallocates the transmission resource to the logical channels on whichcontention-based uplink grant is allowed in order of priority at step637. Once the LCP process completes at steps 635 and 637, the UE 505determines whether to perform the contention-based uplink transmissionas step 640. At step 640, the UE 505 determines whether the uplinktransmission power required for uplink transmission according to thecontention-based uplink grant is greater than a reference value and, ifso, the procedure goes to step 655 and, otherwise, step 645. Thereference value is a threshold value for determining inefficiency whenthe uplink transmission power is greater than the threshold value, e.g.maximum transmission power of the UE 505. Or, it can be a predeterminedrate of the maximum transmission power of the UE 505. The UE 505compares the amount of the padding bits to be included in the MAC PDU tobe transmitted in uplink transmission according to the contention-basedgrant with a predetermined reference value at step 645 and, if theamount of the padding bits is greater than the reference value, gives upthe uplink transmission at step 655 and otherwise if the amount of thepadding bits is equal to or less than the reference value, generates andtransmits a MAC PDU at step 650. The reference value is the thresholdvalue for determining the inefficiency of the uplink transmission, whenthe amount of the padding bits is greater than the threshold value, andcan be set to a certain value by the a network operator. If paddingoccurs, this means basically that the uplink transmission is inefficientsuch that it is possible for only the UE having the data large enough tobe transmitted without padding to perform the contention-based uplinktransmission by setting the reference value to 0 byte. Also, thereference value can be set to an integer according to the resourcemanagement policy of the network operator or an occupancy rate of thepadding in the MAC PDU. For example, it can be configured for thecontention-based uplink transmission to be performed when the padding isequal to or less than n bytes or the occupancy rate of the padding inthe MAC PDU is equal to or less than m %.

Second Embodiment

FIG. 7 is a signaling diagram illustrating a contention-basedtransmission procedure according to the second embodiment of the presentinvention.

A description is made of the contention-based transmission procedureaccording to the second embodiment with reference to FIG. 7. If severalresources are left without use at a certain time point, the eNB maygenerates several contention-based grants simultaneously. As aconsequence, the UE may receive several contention-based uplink grantssimultaneously. At this time, the UE has to select one uplink grant inany way. The simplest method is to select an uplink grant randomly.Although the random selection is simple, it is not a good way in view ofthe transmission efficiency.

In order to overcome this, in the second embodiment, when multiplecontention-based uplink grants are received simultaneously, the UEselects the contention-based uplink grant allowing the largest amount ofdata transmission. If there are multiple contention-based uplink grantsfulfilling this condition, the UE selects an uplink grant inconsideration of its channel state. In the system selecting thecontention-based uplink grant allowing the largest amount of datatransmission, the contention-based uplink grant indicating the largestamount of data transmission is likely to be selected by multiple UEs.The eNB applies a high channel coding rate to the uplink grant signalsuch that the contention-based uplink grant indicating the largest datatransmission amount is selected by the UEs having good channel states.Likewise, the eNB applies a low channel coding rate to the uplink grantsignal such that the contention-based uplink grant indicating low datatransmission amount is selected by the UEs having bad channel states aswell as the UEs having the good channel states.

For example, suppose that the UE 1 710 has good channel state, the UE 2705 has band channel state, and the eNB 715 transmits a contention-baseduplink grant indicating data amount of 200 bytes in a certain subframeand another contention-based uplink grant indicating data amount of 1000bytes. In this case, the eNB 715 transmits the 1000-byte grant with lowreliability at step 720 such that only the UE 710 having good channelstate can receive. Meanwhile, the eNB 715 transmits the 200-byte grantwith high reliability at step 725 such that the UEs 705 having bandchannel state can receive too. The UE 1 710 having good channel statereceives both the 200-byte grant and 1000-byte grant and selects the1000-byte grant allowing relatively large amount of data transmission(730). Meanwhile, the UE 2 705 having band channel state receives onlythe 200-byte grant and selects the 200-byte grant with no choice (735).

FIG. 8 is a flowchart illustrating a procedure of the UE according tothe second embodiment of the present invention.

If multiple contention-based uplink grants are received at step 805, theUE 705 or 710 calculates the data amount to be transmitted based on thecontention-based uplink grants and input the value to the variable X.for example, the data amount indicated by the contention-based uplinkgrant may be the total amount of the transmittable data stored in thelogical channel on which the contention-based uplink transmission. TheUE 705 or 710 selects the uplink grant closest to x in transmission dataamount among the uplink grants passed validity test at step 815. Forexample, if the data amount transmittable in contention-basedtransmission mode is 100 bytes, if four contention-based uplink grantsare received, if one contention-based uplink grant indicates 50 types ofdata transmission, and if the other three uplink grants indicate 90bytes of data transmission, the UE 705 or 710 selects thecontention-based uplink grants indicating the data amount of 90 bytesthat are closest to the 100 types. The UE 705 or 710 determines whethermultiple contention-based uplink grants are selected at step 820. Ifonly one contention-based uplink grant is selected, the UE 705 or 710selects the contention-based uplink grant at step 825 and performsuplink transmission according to the selected uplink grant. If multiplecontention-based uplink grants are selected, the UE 705 or 710 selectsone of the multiple contention-based uplink grants at step 830. At step830, the UE 705 or 710 determines whether the current channel conditionis better than a predetermined reference value. The reference value maybe notified to the UE 705 or 710 in call setup procedure. The channelcondition can be determined based on a pathloss value. For example, ifthe pathloss is greater than the reference value, this means bad channelcondition and, otherwise if the pathloss is less than the referencevalue, this means good channel condition. If the channel condition isworse than the reference value, the UE 701 or 710 goes to step 840. Ifthe channel condition is bad, this means that the UE 705 or 710 islocated at the cell edge such that the high transmission power may causeinterference to other cells. In order to minimize the interference toother cells, the UE 705 or 710 selects one of the contention-baseduplink grants randomly with the exception of the contention-based uplinkgrant indicating the highest transmission power. The contention-baseduplink grant indicating the highest transmission power is the uplinkgrant requiring small resource amount and high MCS level. If therequired transmission powers of the selected contention-based uplinkgrants are identical among each other, i.e. require the sametransmission resource amount and MCS level, the UE 705 or 710 selectsone of the selected contention-based uplink grants. If the channelcondition is better than the reference value, the UE goes to step 835.At step 835, the UE 705 or 710 selects one of the grants randomly, withthe exception of the contention-based uplink grant indicating the lowestrequired transmission power, in order to avoid increase of the selectionprobability of the grant indicating low required transmission power. Ifthe required transmission powers indicating the selectedcontention-based uplink grants are identical among each other, the UE705 or 710 selects one of all the selected contention-based uplinkgrants.

FIG. 9 is a flowchart illustrating a procedure of the UE 715 accordingto the second embodiment of the present invention.

If multiple contention-based uplink grants transmission necessity occursat step 905, the eNB 715 goes to step 910. For example, if the resourcesremained without use are distributed over multiple frequency bands, theeNB 715 may determines that the multiple contention-based uplink grantstransmission necessity has occurred. The eNB 715 determines the MCSlevel of the contention-based uplink grant such that the transmissiondata amount to be indicated by the contention-based uplink grant and thereliability of the uplink grant are inversely proportional with eachother. For example, a high MCS level is determined for thecontention-based uplink grant indicating 1000-byte data transmissionwhile a low MCS level is determined for the contention-based uplinkgrant indicating 200-byte data transmission. The eNB transmits thecontention-based uplink grant with the determined MCS level at step 915.

Third Embodiment

Typically, the random access procedure performed to transmit animportant control message. The random access procedure is composed oftransmitting a Random Access Preamble, receiving a Random AccessResponse message, and transmitting message 3. The UE which is in themiddle of or initiating the random access procedure may receive acontention-based uplink grant. If the contention-based uplink grant forperforming contention-based uplink transmission is received in thesubframe carrying the Random Access Preamble or message 3, the UE has todetermine whether to continue the random access procedure or initiatethe contention-based uplink transmission.

The third embodiment of the present invention proposes a UE operationwhen the uplink transmission required in the random access procedure isoverlapped with the contention-based uplink transmission.

FIG. 10 is a flowchart illustrating a procedure of the UE according tothe third embodiment of the present invention.

If the contention-based uplink grant is received at step 1005, the UEchecks whether the subframe carrying the uplink transmission isidentical with the subframe carrying the message 3 at step 1010. If thetwo subframes are identical with each other, the UE determines that thereceived contention-based uplink grant is an invalid uplink grant andgives up the contention-based uplink transmission at step 1030.

If the subframe for uplink transmission and the subframe fortransmitting the message 3 differ from each other and if thecontention-based uplink grant is selected, the UE performs validity teston the contention-based uplink grant by comparing the padding bitsamount to occur and uplink transmission power with respective referencevalues at step 1015. If it is determined that the receivedcontention-based uplink grant is valid, the procedure goes to step 1020and, otherwise if it is determined that the contention-based uplinkgrant is invalid, step 1030.

At step 1020, the UE determines whether to transmit the preamble in thesubframe in which contention-based uplink transmission is performedright before the contention-based uplink transmission. If the randomaccess procedure is triggered due to a certain reason, the UE transmitsthe Random Access Preamble in the subframe closest to the correspondingtime point among the subframes capable of transmitting the Random AccessPreamble. The random access procedure can be triggered at any time suchthat the check on whether the contention-based uplink transmission andthe Random Access Preamble transmission are scheduled in the samesubframe is performed at an imminent timing of the contention-baseduplink transmission.

If the contention-based uplink transmission and the Random AccessPreamble transmission are scheduled in the same subframe, the UE givesup the contention-based uplink transmission at step 1030 and, if theRandom Access Preamble transmission is not scheduled in the subframe inwhich the contention-based uplink transmission is scheduled, the UEperforms the contention-based uplink transmission at step 1025.

Fourth Embodiment

In order to transition to connected state, the UE in idle statetransmits an RRC CONNECTION SETUP REQUEST message to the eNB. The UE inconnected state but temporarily in service failure state transmits aCONNECTIONE REESTABLISHMENT REQUEST message to the eNB in order torecover the connection. If these messages are transmitted throughcontention-based access, it is likely to fail transitioning to theconnected state or recovering the connection due to transmissionfailure.

In the fourth embodiment of the present invention, if transmission dataoccur, the UE determines whether there is SRB 0 data currently inwaiting for transmission. If there is SRB 0 data in waiting fortransmission, the UE gives up the contention-based access for preventingthe data from being transmitted in contention-based mode. If there is noSRB 0 data in waiting for transmission, the UE starts the procedure forcontention-based access.

FIG. 11 is a flowchart illustrating a procedure of the UE according tothe fourth embodiment of the present invention.

If transmittable data occurs in the UE at step 1105, the UE determineswhether there is the data to be transmitted on the SRB 0 at thecorresponding timing at step 1110. Since the SRB 0 is the logicalchannel having the highest priority among all the logical channels, if acontention-based uplink grant is received while the SRB 0 data is inwaiting for transmission, the UE transmits the SRB 0 data incontention-based mode through normal logical channel selection process.In order to prevent this, the UE goes to step 1115 when there is thedata to be transmitted on the SRB 0.

At step 1115, if it is monitoring CB-RNTI, the UE stops monitoringCB-RNTI. In other words, the UE stops receiving the contention-baseduplink grant. Although not depicted in drawing, the UE may performrandom access procedure to the eNB after stopping monitoring of theCB-RNTI.

Otherwise, if there is no data to be transmitted on SRB 0, the UEdetermines whether a CB-RNTI monitoring condition is fulfilled at thecorresponding timing at step 1120.

If the CB-RNTI monitoring condition is fulfilled, this means that thenecessity of the use of the contention-based uplink grant is high. Forexample, this is the case that the UE has retained the data having ahigh priority for long time duration or the data having a high priorityoccurs newly.

If the CB-RNTI monitoring condition is not fulfilled, the procedure goesto step 1115 and, otherwise, step 1125. At step 1125, the UE monitorsthe CB-RNTI. If the UE monitors CB-RNTI, this means that the UE monitorsthe receipt of the uplink grant addressed by the CB-RNTI on the downlinkcontrol channel. Although not depicted in drawing, the UE may transmitthe data to the eNB according to the resource allocation information ofthe received contention-based uplink grant.

Fifth Embodiment

The UE transmits a Buffer Status Report message (BSR) to the eNB inorder for the eNB to allocate the uplink transmission resourceefficiently. The buffer status report message is categorized into one ofa period buffer status report message and a regular buffer status reportmessage. The periodic buffer status message is triggered when the timerstarting with the transmission of the buffer status report messageexpires, and the regular buffer status report message is triggered whendata having the priority higher than that of the data stored in the UEcurrently occurs.

Since the regular buffer status report message is more important thanthe periodic buffer status report message, if the regular buffer statusreport is triggered, the UE requests the eNB for transmission resourceallocation for immediate transmission of the regular buffer statusreport. Meanwhile, if the periodic buffer state report is triggeredwithout SR, the periodic buffer status report is transmitted in theuplink transmission according to the uplink grant transmitted firstafter the periodic buffer status report has been triggered.

The periodic buffer status report or the regular buffer status reporthas to be transmitted as immediate as possible and assigned hightransmission reliability. If putting weight on the quick transmission,it is preferred to transmit the buffer status report in contention-baseduplink transmission and, otherwise if putting weight on the transmissionreliability, it is preferred to giving up the buffer status report inthe contention-based uplink transmission.

In the fifth embodiment of the present invention, the periodic bufferstatus report and the regular buffer status report are carried in thecontention-based uplink transmission and retriggered after completion ofthe contention-based uplink transmission immediately in order to satisfyboth the two conditions above.

FIG. 12 is a flowchart illustrating a procedure of the UE according tothe fifth embodiment of the present invention.

After determining uplink transmission at step 1205, the UE generates andtransmits a MAC PDU at step 1210. The UE determines whether the uplinktransmission has been contention-based transmission at step 1215. If theuplink transmission has not been contention-based transmission, the UEoperates according to the legacy technology at step 1240 and, otherwise,goes to step 1220. At step 1220, the UE determines whether the periodicBSR has been carried in the uplink transmission. If the periodic BSR hasbeen carried, the procedure goes to step 1225 and, otherwise, step 1230.At step 1225, the UE retriggers the periodic BSR to guarantee thetransmission reliability of the periodic BSR. That is, the UE sends theMAC PDU including the periodic BSR in the next uplink transmission. Atstep 1230, the UE determines whether the regular BSR has been carried inthe uplink transmission. If the regular BSR has been carrier, theprocedure goes to step 1235 and, otherwise, step 1240. At step 1235, theUE retriggers the regular BSR to guarantee the transmission reliabilityof the regular BSR. That is, the UE triggers SR to request the eNB foruplink transmission resource allocation and performs uplinkretransmission carrying the MAC PDU including the regular BSR.

Sixth Embodiment

Since the contention-based transmission has low transmissionreliability, the transmission failure probability is high and thus it isimportant to check quickly whether the transmission has succeeded orfailed. The present invention proposes a method and apparatus that iscapable of checking the success or failure of the RLC PDU transmissionin contention-based mode by setting a poll bit of the RLC PDUtransmitted in contention-based mode to 1 without subsequent RLC PDUtransmission.

FIG. 13 is a flowchart illustrating a procedure of the UE according tothe sixth embodiment of the present invention.

The RLC entity generates an RLC PDU at step 1305. The RLC entitydetermines whether to transmit the generated RLC PDU in contention-basedmode. If the RLC PDU is not transmitted in contention-based mode, the UEgoes to step 1315 to operate according to the conventional technologyand, otherwise if the RLC PDU is transmitted in contention-based mode,step 1320. In order to check the transmission success/failure of the RLCPDU sent in the contention-based mode, the UE set the poll bit of theRLC PDU to 1 at step 1320. The poll bit is a predetermined bit of theheader of the RLC PDU and, if the poll bit is set to 1, the counterpartRLC entity generates and transmits the RLC status report message. TheRLC entity saves the sequence number of the RLC PDU having the poll bitset to 1 into a variable called POLL_SN at step 1325. The sequencenumber of the RLC PDU at a certain timing is identical with the valueobtained by subtracting 1 from a variable called VT(S) such that thePOLL_SN is set to the value obtained 1 from the VT(S) at thecorresponding timing. The RLC entity delivers the RLC PDU to a lowerlayer at step 1330 and starts T-pollretransmit.

T_pollretransmit is of guaranteeing the transmission reliability of theRLC PDU own which poll bit is set to 1 such that, if the status reportmessage is not received before the expiry of T_pollretransmit, the RLCentity sets the poll bit of the next RLC PDU to request for the statusreport message again. In the sixth embodiment of the present invention,if the expired T_pollretransmit has run for the RLC PDU transmitted incontention-based mode, the UE retransmits the RLC PDU (having the hightransmission failure probability) transmitted in contention-based modeother than resetting the poll bit.

FIG. 14 is a flowchart illustrating a procedure of the UE in expiry ofT_pollretransmit according to the sixth embodiment of the presentinvention. If T_pollretransmit timer expires at step 1405, the RLCentity goes to step 1410. At step 1410, the RLC entity determineswhether the T_pollretransmit timer has been triggered due to RLC PDUtransmitted in contention-based mode, i.e. if the timer has expired in asituation where the poll bit has been set to 1 while transmitting acertain RLC PDU in contention-based mode with the start of theT_pollretransmit timer. If it is determined that the T_pollretransmittimer has been triggered due to the RLC PDU transmitted incontention-based mode, the RLC entity goes to step 1420. If it isdetermined that the T_pollretransmit timer has been triggered due toother reason than the RLC PDU transmitted in contention-based mode, theRLC entity goes to step 1415.

If the procedure goes to step 1420, this means that the transmissionfailure probability of the RLC PDU transmitted in contention-based modeis high such that the RLC PDU having the poll bit set to 1 andtransmitted in contention-based mode is retransmitted. This is identicalwith the retransmission of the RLC PDU having the sequence number savedin POLL_SN.

At step 1515, the RLC entity sets the poll bit of the RLC PDU to betransmitted next to 1, updates the POLL_SN, and starts T_pollretransmittimer according to the convention technology.

FIG. 15 is a block diagram illustrating the UE according to theembodiment of the present invention.

It is noted that the higher layer entities are not depicted in the UEblock diagram of FIG. 15. The high layer entities may include PDCP andRLC entities activated per logical channel. As shown in FIG. 15, the UEincludes a multiplexer/demultiplexer 1505, an HARQ processor 1510, anSR/BSR controller 1515, a contention-based access controller 1520, and atransceiver 1525.

The contention-based access controller interprets the contention-baseduplink grant received through downlink control channel, determineswhether to UEs contention-based uplink grant, and controls thetransceiver to perform uplink transmission according to thedetermination result. In the first embodiment of the present invention,the contention-based access controller checks the logical channel onwhich contention-based access is allowed and controls, when thecontention-based uplink grant is received, the multiplexer/demultiplexerto perform logical channel selection process in consideration of thedata on the logical channels on which the contention-based access isallowed. The contention-based access controller also determines whetherto perform contention-based uplink transmission in consideration of thepadding bit state of the MAC PDU to be generated and the uplinktransmission output state.

In the second embodiment of the present invention, if multiplecontention-based uplink grants are received, the contention-based uplinkaccess controller selects the uplink grant indicating the size closestto the data amount to be carried in contention-based uplink transmissionand controls the multiplexer/demultiplexer and the transceiver toperform uplink transmission according to the grant.

In the third embodiment of the present invention, the contention-baseduplink access controller monitors whether the contention-based uplinktransmission collide with the message 3 transmission or the preambletransmission and, if collision is detected, controls themultiplexer/demultiplexer and the transceiver to give up thecontention-based uplink transmission.

In the fourth embodiment of the present invention, the contention-baseduplink access controller determines whether to perform thecontention-based uplink transmission depending on whether SRB 0 dataexists.

In the fifth embodiment of the present invention, the contention-baseduplink access controller controls the SR/BSR controller to trigger theBSR again when the periodic BSR or the regular BSR is transmitted incontention-based mode.

The SR/BSR controller monitors the occurrence of high layer data todetermine BSR trigger. If BSR is triggered, the SR transmissionprocedure is triggered. Also, the SR/BSR controller triggers theperiodic BSR or regular BSR according to the instruction of thecontention-based uplink access controller.

The transceiver 1525 of the UE is the device for transmitting/receivingMAC PDU or control information through a radio channel. The transceiveris the device for receiving HARQ packets. The HARQ processor 1510 is aset of soft combining buffers for performing HARQ operation andidentified by HARQ process identifier. The multiplexer/demultiplexerperforms logical channel selection process and notifies of thetransmission data amount per logical channel. themultiplexer/demultiplexer also combines the data received throughmultiple logical channels to generate a MAC PDU or demultiplexes the MACPDU into MAC SDUs to deliver to appropriate logical channel.

FIG. 16 is a block diagram illustrating the UE RLC entity according tothe sixth embodiment of the present invention.

The RLC entity includes an RLC transmission buffer 1605, an RLC headerinserter 1610, an RLC retransmission buffer 1615, a polling bitconfigurator 1620, and a polling controller 1625, and is connected to amultiplexer/demultiplexer 1630.

The RLC transmission buffer is the buffer for buffering PDCP PDUs and,when RLC PDU is generated, aggregates the PDCP PDUs in match with thepayload size of the RLC PDU or delivers a part to the RLC headerinserter. The RLC header inserter inserts predetermined header fields(RLC sequence number, length indicator, etc.) in the payload of the RLCPDU to generate the RLC PDU. The RLC PDU generated by the RLC headerinserter is delivered to the polling bit configurator and the RLCretransmission buffer. The RLC retransmission buffer retransmits thecorresponding PDU in response to the specific RLC PDU retransmissioninstruction from the polling controller or the state retransmissioncontroller (not shown).

The polling controller controls the polling bit configurator to set thepolling bit of the RLC PDU satisfying a predetermined condition to 1.The predetermined condition can be the contention-based transmission ofthe RLC PDU. If the RLC PDU of which polling bit is set to 1 isdelivered to the lower layer, the t-pollretransmit starts. If thet-pollretransmit expires and if the RLC PDU has triggered thet-pollretransmit, the polling controller controls the RLC retransmissionbuffer to retransmit the RLC PDU corresponding to the POLL_SN.

FIG. 17 is a block diagram of the eNB according to an embodiment of thepresent invention.

It is noted that the higher layer entities is not depicted in the eNBblock diagram of FIG. 17. As shown in FIG. 17, the eNB includes amultiplexer/demultiplexer 1705, an HARQ processor 1710, a transceiver1715, a contention-based uplink grant controller 1720, and a scheduler1725.

The contention-based uplink grant controller determines whether toallocate resource using contention-based uplink grant in considerationof the uplink transmission resource status. The contention-based uplinkgrant controller determines the MCS level to be adopted to thecontention-based uplink grant. The contention-based uplink grantindicating large amount of data transmission is transmitted at high MCSlevel such that only the UEs having good channel conditions can receivethe uplink grant while the contention-based uplink grant indicatingsmall amount of data transmission is transmitted at low MCS level suchthat the UE having bad channel conditions may receive too. Thecontention-based uplink grant controller notifies the scheduler of thecontention-based uplink grants determined for resource allocation andthe MCS levels applied to the respective grants. The schedulerdetermines the UEs and uplink transmission resource in consideration ofthe priorities and amounts of the reported uplink data and generates theuplink grants to the transceiver according to the determination results.At this time, the scheduler generates the contention-based uplink grantsrequested for transmission by the contention-based uplink grantcontroller to the transceiver. The scheduler controls the transceiver toapply the appropriate MCS levels for the respective uplink grants. Thescheduler also controls the transceiver to receive and decode the uplinktransmission indicated by the uplink grant. If there is the uplinktransmission resource left after scheduling, the scheduler notifies thecontention-based uplink grant controller of this.

The transceiver 1715 is the device transmits and receives MAC PDUs orcontrol information through a radio channel. The HARQ processor 1710 isa set of soft combining buffers for performing HARQ operation andidentified by HARQ process identifier. The multiplexer/demultiplexercombines the data received through multiple logical channels to generatea MAC PDU or demultiplexes the MAC PDU into MAC SDUs to deliver toappropriate logical channel.

While the invention is described in terms of some specific examples andembodiments, it will be clear that this invention is not limited tothese specific examples and embodiments and that many changes andmodified embodiments will be obvious to those skilled in the art withoutdeparting from the true spirit and scope of the invention.

What is claimed is:
 1. A method for performing an uplink transmission bya terminal in a mobile communication system, the method comprising:receiving, from a base station, first configuration information of afirst logical channel and second configuration information of a secondlogical channel, the first configuration information of the firstlogical channel indicates whether data of the first logical channel isallowed to be transmitted on a contention based resource, and the secondconfiguration information of the second logical channel indicateswhether data of the second logical channel is allowed to be transmittedon the contention based resource; receiving an uplink grant from thebase station; identifying that first data of the first logical channelis not allowed to be transmitted on the contention based resource basedon the first configuration information, and second data of the secondlogical channel is allowed to be transmitted on the contention basedresource based on the second configuration information; determiningwhether the uplink grant is for a transmission on the contention basedresource; transmitting, to the base station, the first data of the firstlogical channel and the second data of the first logical channel usingthe uplink grant based on the determination that the uplink grant is notfor the transmission on the contention based resource; and transmitting,to the base station, the second data of the second logical channel usingthe uplink grant based on the determination that the uplink grant is forthe transmission on the contention based resource.